Low-mass short-stroke voice-coil actuator for integrated disk file module

ABSTRACT

A low-mass low-inductance short-stroke voice-coil actuator used with a positionable transducer and magnetic disk to provide fast memory access in a low cost-per-bit disk file memory system. Enclosed in a sealed disk module, the actuator and transducing system provide access to any disk information track within one disk revolution or less. Integral with said actuator is a total moving mass of less than 50 grams. A short voice-coil, of one inch or less, is always contained within the magnetic flux of the air gap; and the voice-coil, when energized, can provide a full stroke access (across said magnetic disk) within 16 milliseconds. A pair of spider flexures support (for longitudinal movement) a central rod, which is part of a differential velocity transducer and which is integral with the voice-coil. The central rod is also capable of being rotated by a solenoid to turn a cam which will &#34;unload&#34; or remove the transducing heads away from the disk surfaces.

FIELD OF THE INVENTION

The voice-coil actuator of the present invention pertains to the fieldof random-access disk drives permitting very low cost-per-bit storageand access, wherein the voice-coil actuator has a short stroke motionand provides fast access due to the small mass moved. The actuator hasparticular use in combination with a sealed Disk File Module and memorysystem also described herein.

BACKGROUND OF THE INVENTION

The desirability of disk file units which can readily be removed andreplaced or interchanged with other units has long been recognized.

However, some liabilities have occurred in the prior art in attemptingto achieve this goal in that expensive and unwieldy "base units" wereoften required which would mechanically interconnect to the disk modulein order to provide a driving force (for the disk pack and headcarriage) through a shaft or a belt, at the same time attempting to sealoff any contamination from the outside air or environment. This wastypically the case in the "Winchester" disk unit as described in U.S.Pat. No. 3,843,967. These type of disk units, further, were not readilyadaptable for use with the power frequencies of foreign countries (suchas 50 Hz.) nor aircraft power at 400 Hz.

Other prior art attempts have been made in this area by providing sealedenclosures with transducers having head-per-track configurations. Theseusually proved to be extensively expensive and uneconomical.

The use of high-capacity random-access disk drives which permit operatorinterchangeable disk packs has usually been burdened with excessivecosts. The interchangeability costs include additional controlelectronics and hardware for disk pack loading-and-unloading, forstringent contamination protection, for actuator carriage retraction,for head unloading, and adding mechanical couplings for spindle and headcarriage driving. In order to offset these high costs, prior art diskdrives are designed for very high capacity using many stacked disks andrequired relatively large drive motors having high power consumption;thus they were not really economically usable by a medium-to-small scalestorage system.

One of the major costs of designing-in disk pack interchangeability(while keeping medium to low capacity storage) lies primarily in thealignment of the disk unit's transducing Read/Write heads, which mustfly precisely relative to the disk surface. The head-to-disk trackalignment must be sufficiently accomplished so that a disk unit, oncewritten, may be removed and subsequently read on any of the other diskdrive units. Thus, radial alignment of the transducing head with respectto the record track on the disk must be within 20% of the track width.The radial alignment tolerances must include static tolerancesassociated with head alignment differences between different drives, aswell as dynamic tolerances involved, such as spindle-bearing runout,disk axial runout, actuator carriage bearing runout, thermal drift,vibration, and position accuracy of the access servo system.

Contamination during a disk pack exchange can have a serious effect onthe reliability of a disk drive. When the disk pack module is removedfrom its "base drive," then the disk chamber, the disk pack mountingcone, and the transducing Read/Write heads (which are the most sensitiveparts of the drive) are completely exposed to the environment.

Since the transducing heads often fly as close as 25 microinches to thedisk surface, particles not visible to the naked eye, can causedisastrous failures.

In order to overcome some of the above problems and limitations, certainmanufacturers built the "Winchester" disk cartridge, where diskcartridges were made to contain certain critical components (spindle,disk, read/write transducing heads, and an "actuator carriage") in anenclosed package.

This type of packaging somewhat reduced the costly positioningrequirements for radial alignment and also facilitated greater track andbit density then was previously possible. Also at the same time, thereliability was greatly enhanced. However, since the "Winchester" diskcartridges did not contain the actuator voice-coil motor nor thespindle-motor, it was necessary that additional complex hardware beadded to each disk cartridge, and each cartridge had to be supplied witha "base drive" in order to automatically couple the cartridges'"actuator carriage" to the voice-coil motor and also to couple theinternal spindle to an external motor.

Besides being costly, these external-internal couplings introducedadverse reliability factors due to tolerance requirements, to possiblemechanical failure; they also prevented complete sealing of the diskcartridge itself.

Further the "base drive" units (which were required for each diskmodule) had a cost factor of generally six times the cost of the diskmodule. Thus, if the disk module cost $1500.00, the base drive wouldgenerally cost at least $9000.00.

SUMMARY OF THE INVENTION

A low-mass, fast-access actuator unit is provided for use with acompact, slim-lined, self-contained Disk File Module, which module iscompletely sealed, requires no external mechanical couplings, and whichfacilitates interchangeability since the only coupling required is anelectrical connector. The Disk File Module contains a motorspindle unitwhich has the rotor of the drive motor integrated as one unit with themagnetic disk having a single high-density ferrite film on each surface.

With the sealed enclosure of this preferred embodiment is a short-storke(+ or - 1/4 inch) low power voice-coil motor or "actuator" whichsupports and positions a series of Read/Write transducing heads over thetop surface and bottom surface of the magnetic disk. A head support arm,which holds and positions the transducing heads, is directly connectedto the voice-coil, thereby eliminating the mechanical problems of theprior art which required internal "actuator carriages" which then werecoupled to external actuator carriage drive-means outside of the sealedenclosure.

In the preferred embodiment, additional advantages are obtained by theuse of low-mass transducing heads and the elimination of the massivecarriage means formerly used, permits worst-case access times to occurin less than one rotation (16 milliseconds). Also the Disk File Modulecontains no components subject to friction and wear except for twobearings in the motor-spindle which provide a long, extended life cycleof at least seven years.

The cost-per-bit factor of this preferred embodiment of the Disk FileModule is less expensive than the bit cost in multiple-disk largecapacity systems, and less expensive than prior art small-capacitysystems which required actuator carriages and extensive mechanicalcoupling hardware such as was required in the "Winchester" diskcartridge; at the same time, the expensive "base drive" unit has beeneliminated in favor of an "Electronics Module" which provides controlsignals and a data-interface to the Disk File Module.

Further, this elimination of the entire base-drive mechanism, (such asthe drive motor, drive pulley and exterior connecting mechanisms asexemplified by the Winchester system) thus reduces the overall amount ofmanufacturing usage and maintenance costs of the Disk File Module systemwhile the reliability and the versatility of application is increased.

Since the motor drive unit is concentric with the center of the magneticdisk, and the rotor is integrated with the disk to form a substantiallyplanar structure, the overall volume required is economically small andpresents a slender thin-line package. Further, since the module onlyrequires a low power motor unit (1/100 horsepower), it can be easilymade independent of AC line power frequency variations. This is done byusing a crystal-controlled internal frequency reference in theElectronics Module which powers the disk drive motor independent of ACline power frequency.

The voice-coil actuator in this preferred embodiment of a Disk FileModule has approximately ten times less mass than prior art actuatorsand has a voice-coil one-fourth the axial length of prior art coils. Thelow mass and high conductivity permits small control currents to developvery fast access time in seeking the desired track on the disk.

One of the economies provided by the preferred embodiment of the DiskFile Module described herein is the factor of interchangeability. Thefactor of interchangeability of a Disk File Module makes possible greateconomy of manufacture and usage, the convenience of easy maintenance bysimply interchanging a module and the lower cost of maintenance time.Additionally the design of the hardware elements and the tolerancesinvolved in the mechanical, electronic and magnetic implementation ofthe Disk File Module has been so arranged that the summation of all ofthe deviations from perfection does not exceed the total varianceallowed for engineering tolerances.

Further, the sealed Disk File Module prevents any exposure orcontamination of the internal atmosphere and the precisely definedpositions and locations of the mechanical components in relationship tothe disk.

Still further the preferred embodiment offers significant advantagesover conventional type of disk file recording systems which are solelydedicated to "head-pertrack" transducing systems. These conventionalsystems involve many hundreds of transducers and complex matrixswitching networks which are very costly, even though they permit theelimination of moveable transducing heads and actuators. However, in thepresently described embodiment, the actuator's moveable arms andtransducers, in conjunction with the reference position tracks of themagnetic disk, provide for an economical, yet at the same time precise,position seeking system which is sufficiently easy to duplicate andthus, to make interchangeable for each of a plurality of modules. Andyet, in the instant system described herein, there is permitted theversatility of using both positionable and fixed head-per-tracktransducers singly or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cutaway view in elevation of the Disk File Module.

FIG. 2 is a top or plan view of the Disk File Module with thetransparent cover through which can be seen the disk.

FIG. 3 is a cross section view in elevation of the motor-spindleassembly showing how the disk is integrated with the rotor.

FIG. 4A is a schematic cross section view of the voice-coil actuatorassembly used to position the transducing heads.

FIG. 4B shows a top view of the spider flexure for the actuator.

FIG. 4C is a perspective sketch of the upper and lower transducingplatform support arms in the loaded position (transducers on magneticdisk).

FIG. 4D shows the unloaded position of the platform support arms(transducers moved away from magnetic disk).

FIG. 5 is a schematic view of the entire Disk File Module system andindicating the electrical interconnection between the Electronics Moduleand the two Disk File Modules it services.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-3, there is seen one preferred embodiment of theintegrated Disk File Module, wherein a sealed module 10 is formed of abase plate casting 10_(b) (having a transparent top plate 10_(a)) and asheet metal enclosure 8. A motor-spindle unit 20 has holding plates20_(p) which hold and support a magnetic disk 11.

The casting 10_(b) has flanges 7_(f1), 7_(f2), 7_(f3), 7_(f4), (FIGS. 1,2) of which 7_(f3) supports an Actuator Unit 30 which is generally ofthe voice-coil actuator type. A group of transparent inspection plates10_(p) is built into the casting 10_(b) for inspection purposes. TheActuator 30 (FIGS. 1, 4A) will be seen to have a rotary solenoid 43while providing a head support arm 40 (having arms 40_(u) and 40_(l) inFIG. 1 and FIG. 4A) which hold a plurality of Read/Write transducingheads 41 in close proximity to the upper and lower surfaces of the disk11. An electrical connector 50 (FIG. 1) which conveys electrical signalsinto and out of the sealed module is the only connection to the outsideworld of the Disk File Module. A more detailed description is providedin conjunction with the discussion of FIGS. 4A, B, C, and D.

The motor-spindle unit 20, with its support plates 20_(p) for holdingthe disk 11 forms an integral rotating unit which also has a series ofair circulating fins 26 and a cylindrical encoder 27 having indiciamarks 27_(i), which move in proximity to a mark sensor 45. The rotor21_(r) (of FIG. 3) constitutes a cylindrical nickel-cobalt form whichrevolves about stator 22.

Referring to FIG. 2 which shows a top or plan view of the Disk FileModule, the module 10 is seen to have a sheet metal enclosure 8, abase-plate casting 10 wherein three shock mounts 5_(a), 5_(b) and 5_(c)provide resilient support to the sealed module within the sheet metalcovering 8.

The spindle unit 20, having fins 26 and a support plate 20_(p) hold thecircular disk 11 via screws 20_(w). A series of transducer heads 41 aresupported by the head support arm 40 which is controlled by the Actuator30 for the positioning of the heads radially along the disk 11.

Referring to FIG. 3, a central cross sectional view in elevation isshown of the motor-spindle assembly unit 20. A central shaft 21_(s) issupported by a top bearing 23 and a bottom bearing 24 which bearings areheld by the support frame 25.

The support frame 25 mounts the stator core and windings 22, aroundwhich may rotate the rotor unit 21 which is held by a rotor frame21_(f). The rotor 21_(r), the rotor frame 21_(f) and shaft 21_(s)together comprise rotor and shaft unit 21, which is fastened to the disk11 to form an "integrated" rotating unit.

A loading spring 28 preloads the top bearing 23 and bottom bearing 24.

Referring to FIG. 4A, there is seen a central cross section view, inelevation, of the voice-coil Actuator assembly 30. The Actuator assemblyis seen to have a central pole 31 which has an axial bore 31_(b) holdinga differential velocity transducer 34. The velocity transducer has acentral support rod 35 which holds a velocity transducer magnet 36. Thesupport rod 35 is built with extremity extensions 35_(a), 35_(b) heldwithin front and rear spider flexures 38 and 39.

A voice-coil bobbin 37_(b) holds a cylindrical voice-coil 37 which ridesin the gap between the central pole 31 and the laminated pole pieces 33of the ring magnet 32. The voice-coil 37 has high conductivity and itsaxial length is small compared to the air gap 33_(g) between the polepieces of elements 33 and 31. Thus during its 1/4 inch stroke, thevoice-coil never comes near or passes beyond the fringes of the air gap.

By regulating the current through the voice-coil 37 the head support arm40 will move to precisely regulated positions along the tracks of themagnetic disk 11. More details of the Actuator 30 will appear in thelater detailed discussion of FIG. 4A.

A rotary solenoid 43, designated as the load/unload solenoid, is capableof rotating the central support rod 35 which connects to a cam 42 at theopposite end. The cam 42, when rotated, is capable of positioning thetransducing heads 41 away from the surface of the magnetic disk 11. Thisload/unload cam 42 is arranged so as to control the upper transducingheads 41_(u) as well as the lower transducing heads 41₁ (FIG. 1), aswill be later described in detail.

FIG. 5, which will be described in detail hereinafter, shows the overallmemory storage and access system by which one Electronics Module 50Eprovides control and service to two Disk File Modules 10 and 10'.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2 which respectively show a simplifiedcross-sectional view and a simplified top view of the Disk File Module,it will be seen that a thin-walled ribbed die-cast aluminum base plate10_(b) may typically provide structural support as well as enclosure forthe motor-spindle 20, disk 11, transducer heads 41 and head-positioningarm 40. Visual inspection is provided for by a transparent top cover10_(a) which is held by the sheet metal enclosure 8.

The mounting flanges 7_(fl), 7_(f2), 7_(f3), 7_(f4), on the side wall ofthe base plate 10_(b) may support a single voice-coil Actuator 30, ormay support a plurality of actuators, such as voice-coil Actuator 30.Further, the four flanges may be used for a combination of transducingsystems involving both positionable type and head-per-track type oftransducing systems without the exclusive requirement of a fullycomplete (and costly) head-per-track transducing system.

In a typically preferred embodiment the overall dimensions of the DiskFile Module may be approximately 4 inches high by 15 inches wide by 18inches deep and the total weight is less than 20 pounds. An electricalconnector 50 is used to facilitate automatic electrical hook-up when theDisk File Module is plugged into its mounting rack in the ElectronicModule 50E (FIG. 5).

Referring to the motor-spindle assembly 20 which is shown in FIG. 3,this structure is made of a fixed stator portion 22 and a rotatableportion 21 which comprises rotor 21_(r) and rotor frame 21_(f) inaddition to the rotor shaft 21_(s). The motor may typically be aone/one-hundredth horsepower, 12 volts AC synchronous hysteresis motor,which can operate in the range of 2400-3600 rpm.

The preload spring 28 exerts pressure on precision bearings 23 and 24which may be of a type having a minimum continuous duty life of 7 years.Such bearings are basically the only components of the Disk File Modulesubject to friction and wear and thus are made of high quality precisioncomponents.

The motor speed is precisionally controlled by a motor spindle control53 using a Crystal Reference Unit in the Electronic Module 50E (FIG. 5)which may typically be set to control the motor rotation at 3600 rpm.The speed may be simply changed to 2400 rpm by switching to a differentreference frequency. This permits unusual versatility over the prior artsystems where a speed change involved complex changes in gearing andbelt drives. Thus, rapid data-transfer rates can be handled in thisembodiment by the higher 3600 rpm speed while low speed data-transferrequirements are handled by the 2400 rpm rotational speed.

While prior systems customarily required 1/3 horsepower (or more) motorsto drive a grouped stack of magnetic disks (in order to get large datacapacity per unit so as to lower the cost-per-bit of handling diskdata-storage) the present system permits a low power motor consuming,for example, 10 watts or less and occupying a relatively small volume.Typically a Disk File Module and system in accordance with the inventionprovides a low cost-per-bit function of approximately 0.5 millicent perbit which is at least two times cheaper in cost-per-bit functions thandisk systems of the prior art. Further this low cost-per-bit capacity iscontained in a spatial slim-line volume approximately one-half the sizeof prior Disk File Modules. Thus, there is provided not only an optimalcost-per-bit but also optimal size per overall bit capacity. Furtheroptimization occurs in that one Electronic Module, as 50E (FIG. 5),services two or more Disk File Modules rather than an expensive "baseunit" for each single disk module as required previously.

The synchronous motor used herein may typically operate at 12 volts RMSat a 120 cycle regulated frequency. It is independent of AC power linevariations due to the internal frequency reference unit in theElectronic Module 50E. The rotor 21_(r) is a cylindrical form ofnickel-cobalt having a plate 20_(p) which integrates the rotor with thedisk 11 to constitute a unitary rotational unit.

In the cross sectional view of FIG. 4A there is seen the voice-coilActuator assembly 30. The head mounting platform or head support arm 40shown in FIG. 4A is actually made up of an upper arm 40_(u) and a lowerarm 40_(l) (See FIGS. 1 and 4C) and these arms are directly connected toa short 2-inch diameter voice-coil bobbin 37_(b) of FIG.4A.

A small low-inductance voice-coil 37 is wound on the voice-coil bobbin37_(b). The voice-coil 37 always remains within the air gap 33_(g)between the laminated pole piece 33 and the cylindrical center pole 31.

The actuator has one unitary moving structure composed of the centralsupport rod 35, the voice-coil bobbin 37_(b), annular support ends35_(a) and 35_(b) for the central support rod 35, voice-coil 37, and thehead mounting platform arm 40 with its transducing heads 41.

The center pole structure 31 of magnetic material has an axial bore31_(b) in which resides a metallic magnetic-insulator shield 31_(s).Within the shield 31_(s) there resides a stationary pair of windings31_(w1) and 31_(w2).

Within the axial bore of these windings the central support rod 35 iscapable of straight longitudinal movement via the restrictions of theflexures 38 and 39 (FIGS. 4A and 4B). Within the central support rod 35resides a velocity transducer magnet 36 which together with the windings31_(w1), 31_(w2) constitute a differential velocity transducer 34 forconveying signals relative to position and speed of displacement of thecentral support rod.

The lower end of the central support rod 35 is accessed by a rotarysolenoid 43 through a splined shaft 43_(s). This enables the rotarysolenoid to rotate the central support rod 35 on its axis within theshield 31_(s). Rotation of the central support rod 35 will cause theload/unload cam 42 to be rotated into a different position between theupper and lower head support arms 40_(u) and 40_(l) (FIG. 4C). It willalso be noticed that (in FIG. 4A and 4C) a pivot 40_(p) provides arotational pivot for the upper support arm 40_(u) while a pivot 40_(p) 'provides the pivot for the lowest support arm 40_(l) (FIG. 4D).

FIG. 4B shows a top view of the spider flexures 38 and 39. Acircumferential band 38_(a) supports a series of spiral projections38_(s) which hold a central bearing 38_(b) having an axial bore 38_(n).

The diagrammatic sketch of FIG. 4C indicates how the voice-coil bobbin37_(b) supports the transducing head platform arms 40_(u) and 40_(l).The cam 42 is disengaged from the arms 40_(u) and 40_(l) so that thetransducing heads would be "loaded" i.e. in contact with the surface ofthe disk.

Referring to FIG. 4D, it will be seen that the cam 42 has been turnedbetween the upper and lower head platform support arms to exert turningpressure on the upper and lower arms 40_(u) and 40_(l). This action"unloads" the transducing heads, i.e. removes them away from the surfaceof the disk.

The coaxially-mounted differential velocity transducer 34 has a magnet36 embedded in the suspension-support rod 35; and the entire moving mass(consisting of the transducing Read/Write heads 51, the track followerservo head 41_(s), (FIG. 4A), the upper and lower head mounting arms40_(u) and 40_(l), the voice-coil 37, bobbin 37_(b) and the suspensionrod 35) may typically be approximately 40 grams.

In the preferred embodiment being described in actuator assembly'scenter of mass is exactly in line with the center of force. Theactuator's small mass (which may typically be 30 times less than that ofa "carriage-type" actuator) is suspended by two spring flexures 38 and39 which are similar to loudspeaker "spiders." This small mass,typically, has a total travel of not more than plus or minus one-quarterof an inch. This moving mass, (consisting of 9 Read/Write heads, theservo head, upper and lower arms, the voice-coil, the bobbin, andcentral rod) of typically approximately 40 grams provides a minimum massfactor which permits an access time of less than one disk rotation witha voice-coil motor actuator requiring one-tenth less force thanconventional voice-coil actuators. In physical size the voice-coil motoror actuator assembly is approximately equal to that of a 20 wattloudspeaker driver.

One advantageous feature of the voice-coil actuator of FIG. 4A is thefact that the voice-coil is very short, that is 1 inch or less, and italways remains completely within the total field between the laminatedpole piece 33 and the center pole 31 of the voice-coil actuator. Thismay be contrasted with prior art voice-coils which constituted lengthsof 4 inches or more and in which only a part of the voice-coil remainedwithin the full field of the pole piece 33 and center pole 31. Thus,much of the generated energy was dissipated in heat and further therewas a massive amount of iron and magnetic hardware which was requiredfor long strokes (which may be up to 31/2 to 4 inches where thetransducing heads and head arms are completely retracted away from thedisk and must be moved a relatively long distance in order to reach thedisk and then to recover the radial distance across the disk).

Prior art actuators required that the massive arm and transducing headsbe guided by a group of precision bearings and guide rods. These havebeen completely eliminated in the present embodiment and, since thestroke is typically only ± 1/4 inch or less, the holding system for themoveable central rod 35 is merely a set of spider flexures, (frontflexture 38 and rear spider flexure 39). This eliminates much mass fromthe system and eliminates the conditions whereby bearings (when used)could get contaminated, worn, or stuck due to foreign particles. Aspring flexure such as used here has practically no maintenance problemsover a period of time once the quality of the spring flexure isguaranteed.

The Read/Write transducing heads are conventional flying heads which aredesigned to contact the disk recording surface during starting andstopping, and then "fly" for transducing operations. Since themotor-spindle assembly 20 is not designed for fast acceleration, butinstead is optimized for low weight and minimum power consumption atoperating speeds, the head-to-disk contact time during starting andstopping may be too long for safe long-term operation. This is thereason why the previously disclosed head-loading mechanism is combinedwith the actuator to increase reliability. This head-loading mechanismconsists of a rotary solenoid 43 at the end of the Actuator driveassembly 30 and a cam 42 at the opposite end of the assembly. The rotarysolenoid 43 rotates the central support rod 35 through a normallynoncontacting spline 43_(s). The support rod 35 connects to cam 42 atthe other end of the assembly which causes the upper and lowerhead-mounting arms 40_(u) and 40₁, to rotate slightly and lift the headsoff of the recording surface (FIG. 4D). Each of the head-mounting arms40_(u) and 40₁, are rotatable around a pivot such as pivot 40_(p) shownin FIG. 4D. The cam 42 is a detenting cam so that the rotary solenoid 43only has to be operated during loading and unloading operations. As seenin FIG. 4C and 4D the transducers 41 reside on the head support arms40_(u) and 40₁ in a position farthest away from the side of the headsupport arm which is pivoted at 40_(p) and 40_(p) '.

Thus during the "unloaded" position, as seen in FIG. 4D, the transducingheads 41 are moved outward and away from the magnetic disk 11 whichpasses between the upper and lower head support arms. However, in the"loaded" or the closed position of FIG. 4C, the transducers 41 are nowseen to reside in engagement to the magnetic disk 11 so as tomagnetically contact the surface of the rotating disk.

The central support rod 35 is permitted to rotate in the two spiderflexures 38 and 39, and a heavy spring preload at the pivot pointsprevents servo instability caused by play at the pivot points.

The most critical performance area involves the disk and the Read/Writetransducing heads. In this regard this embodiment uses the field-proven"Winchester" technology whereby the Read/Write transducing head has avery light weight of approximately one-third of a gram and its airbearing requires a force of only 10 grams which facilitates starting andstopping of the head in contact with the disk. The flying height of thetransducing heads is typically approximately 25 microinches and the headhas a ten megahertz resolution. Further, the simplified construction ofthese type of transducing heads contributes to lower costs.

Disk 11, having information tracks 11_(t) is a high density 14 inch dia.disk having ferrite film as the recording medium. As previouslydiscussed, the disk is made as an integrated unit of the rotor portionof the motor-spindle assembly 20. This integrated unit comprises thedisk 11, the holding plate 20_(p), the rotor frame 21_(f), the rotor21_(r) and the shaft 21_(s). The integrated rotor arrangement, placedconcentrically about the stator 22 of the motor-spindle assembly unit20, forms a very slim-lined configuration which saves spatial volume andpresents a compactly balanced unit. The slim-line compactness permits asubstantially planar configuration for the motor drive assembly and itsdisk portion.

In the overall system schematic of FIG. 5, the Disk File Module isconnected by electrical connector 50 to an Electronic Module 50E.

The Electronic Module 50E is separate from the Disk File Module 10 andinterconnects only by electrical cables through connector 50. TheElectronic Module has a number of electronic control components, such asMotor Driver circuit 51 which may conventionally comprise two digitalamplifiers which drive the two windings of the 12 volt AC hysteresissynchronous motor-spindle 20. Both windings conventionally have a seriescapacitor (not shown) to assure reasonant operation. A crystaloscillator and electronic frequency divider (not shown) in theElectronic Module 50E is typically employed in a conventional manner togenerate the two phase-shifted digital motor signals. Since therelatively high current of the actuator voice-coil assembly 30 (which istypically four amperes peak) cannot be multiplexed easily for sharedoperation, a 20 watt hybrid power amplifier is used in the ElectronicModule 50E.

Referring to FIG. 5, the Disk File Module 10 is plug compatible viaconnector 50 to the electronic Module 50E. The Disk File Moduletypically includes a Printed Circuit Board 10_(c) which providedconventional circuitry such as Read Pre-Amp, a Head Switching Matrix anda Write Driver (not shown).

In a manner well known in the art one Electronic Module 50E may handleand service at least two Disk File Modules such as 10 and 10' havingPrinted Circuit Boards 10_(c) and 10_(c) '. Connectors 50 and 50'provide connection from the two Disk File Modules to the singleElectronic Module. Thus, there has been eliminated the requirement for acostly separate "base drive" unit for each Disk File Module.

The Data Channel Control unit 52 may also be a conventional electronicunit which performs level conversion with receiver/drivers for data,clock, address and control signals. The Data Channel Control unit 52provides Read/Write control circuits which are used, for example, inconjunction with the well-known double-density modified-frequencymodulation system for the reading and recording of data on the disk file11.

The Data Channel Control unit 52 typically includes a crystal oscillatorand a phase-lock-loop detector (not shown). The crystal oscillator isused in a conventional manner to control, after proper frequencydivision, the speed of the synchronous motor and is also used togenerate the write clock. Due to the crystal-controlled synchronousmotor, the tracking range of the phase-lock-loop detector will be verynarrow, thus facilitating short lock-in times and therefore reduced gapsizes.

The Motor-Spindle Control unit 53 may be used to control the operationof the motor-spindle assembly 20. The particular low power hysteresissynchronous motor-drive used herein is designed for most efficientoperation at speeds of, for example, 2400-3600 rpm. The rotational speedof this motor is determined by the frequency division signals based fromthe write crystal oscillator. Thus, there is derived a highly accuratemotor-spindle frequency which will permit maximum data rates and maximumbit densities. The motor signals, which are phase-shifted for properoperation of the motor-spindle, are supplied to the two digital motordrivers built into the Electronic Module 50E. The power for the motordrivers is supplied by a DC source, which could be a battery.

It is typically desired to bring the disk 11 up to its proper speedwithin, for example, 60 seconds, and to do so, twice the normal runtorque is needed. Thus, the motor-spindle unit 20 is overdriven with a50% greater voltage during acceleration and deceleration.

The Actuator Servo Control unit 54 which may also be of conventionalform is used to regulate the voice-coil motor actuator assembly 30.

The Read/Write transducing heads 41 are positioned above and below therequired tracks with a dual loop (velocity and position) track followerservo system known in the art. Velocity feedback is generated from theco-axial differential velocity transducer 34, and position feedback isderived from a band of, for example, 251 pre-recorded servo trackslocated on one side of the disk in the middle of the data bands.

As previously mentioned the transducing system may use five uppertransducing heads and five lower transducing heads, one of which is usedas a "servo head." Each head will have a data band of 250 tracks. Thismakes a total of 2,250 information tracks plus 251 servo tracks on agiven disk.

There are many conventional ways for "track seeking" and for servopositioning. One typical way which may be used may be described asfollows. For initialization purposes after the disk file module has beenassembled and sealed, the servo head 41_(s) will be used to record 251servo tracks on the underside of the magnetic disk and each of thesetracks will have its own particular address. If, for example, the firsttrack of a servo track group is contacted by the servo head 41_(s), theservo head will read out information from the first servo track, itslevel will be raised by an amplifier and then fed to a "level logicunit" which will maximize the output signal from the information on theservo track number 1. Then the "level logic output" from the level logicunit will be fed to an "enable decoder." Thus, the signals which wereread out from the track will carry the information of an "address",which information is then fed from the "enable decoder" to a comparator.

The comparator will also have another input of the "desired" trackaddress. Then, as a result of the comparison in the comparator betweenthe desired address and the presently existing read-out address, severalsignals will be developed out of the comparator. One signal coming outof the comparator will be the "magnitude of error" between the twoaddresses which will be used to develop a signal called a "velocityinput signal," which is fed to a "positioning logic unit" which isamplified by an amplifier and used to operate the voice-coil to make itmove in the proper direction of the desired address track.

Another signal coming from the comparator may be called the "directionalsignal" and this signal determines the direction the voice-coil mustmove in order to seek and reach the desired track of the servo trackgroup. Of course, when this direction signal is "zero" this means thatthe voice-coil has already positioned itself over the appropriate servotrack. Usually there is also a signal line from the "level logic unit"over to the positioning logic unit so that the signal read out from theservo track can be maximized and can be fed into the position logicunit. Also there is a direct line from the amplifier of the servo headwhich goes directly to the "enable decoder."

Thus, this "positioning servo" system provides a comparator having twoinputs, one input of which is the track address of the desired track andthe other input of the address of the presently existing track. Thecomparator then provides an output signal to the positioning logic unitand its amplifier which provides the current necessary to move thevoice-coil in the proper direction and at the appropriate speed in orderto most rapidly access the desired track.

Typically each of the transducing heads 41 (and the servo head 41_(s))will have its individual pair of head driver amplifiers and playbackamplifiers.

Each transducing head (and also the servo head 41_(s)), through itsmagnetic pickup provides a signal. This signal is conveyed to a playbackamplifier which may feed to a multiplexer integrated circuit. Themultiplexer integrated circuit may have 9 input lines (for example, onefrom the playback amplifier of each individual transducing head).Further, there may, for example, be three address lines which feed intothe multiplexor integrated circuit to provide a "head address." Thus,the multiplexor (depending on the head address) will connect a line atany given moment of time to the particularly selected transducer head.

Each of the transducer heads also will have another amplifier called the"head driver amplifier" which is used to increase the current to thetransducing head for "writing" purposes; thus, no matter whether thereis a "reading operation" or a "writing operation," there will besufficient current developed so that the transducer head may adequatelywrite on the magnetic disk or may provide an adequate signal when it isreading from the magnetic disk.

The differential velocity transducer 34 (FIG. 4A) provides twostationary windings 31_(w1) and 31_(w2) which, by magnetic induction,are sensitive to motion of the north and south poles of the bar or polemagnet 36 which moves in correspondence with voice coil 37. The windingsof stationary windings 31_(w1) and 31_(w2) are differentially or"contrary" wound so that any motion of pole magnet 36 is enhancedbecause one coil winding picks up motion changes due to the north poleand the other coil winding picks up motion changes due to the southpole. Thus, signals are developed to provide a "velocity" signal to beused as one of the inputs of the servo-amplifier which drives thevoice-coil.

Due to close proximity of the velocity-transducer and the main magneticcircuit for the voice-coil, changes in the voice-coil current andposition could affect the velocity transducer were it not for thedifferentially wound coil windings 31_(w1) and 31_(w2) which cancel outand obviate such extraneous interference.

The "full stroke" access time of the actuator is typically 16milliseconds with an "average" access time of 9 milliseconds while thetrack-to-track access time is 4 milliseconds.

Bit densities on the disk may typically range from 5950 bits-per-inch(BPI) to 8000 BPI. The transfer rates may typically range from 6.5 to9.7 million bits per second.

There are five information bands on one side and four information bandsplus one servo band on the other side of the disk. The total travel ofthe actuator is limited to 250 cylinders (nine information tracks percylinder) or + or - 1/4 inch at 500 TPI (transitions-per inch).

This provides a short-travel, low-mass, closed, and centrally balancedmechanical arrangement which together with low coil induction make itpossible to access any track within 16 milliseconds at one-tenth theforce (7 pounds peak) needed for the conventional type of voice-coilactuators.

Since these actuator controls can be shared between two separate DiskFile Modules, analog switching must be performed to multiplex thefeedback and control signal. However, the peak voice-coil current offour amperes, cannot easily be multiplexed and consequently in thepreferred embodiment considered, a 20 watt hybrid power amplifier isneeded for electrical conveyance to each Disk File Module.

The Read/Write circuit 55 provides, in a conventional manner, controland power for Read/Write transducing operations.

The Maintenance Control unit 56 of conventional form, supplies a poweron/off indicator switch, two sets of load/run indicator switches, awrite protect indicator switch and a Disk File Module address switch(not shown).

The Fail-Safe Control unit 57 provides safety circuits which, in aconventional manner, monitor the module for unsafe conditions that mightcause destruction of information in the event of a component failure orcircuit malfunction. This detection of such a condition would result inan automatic disconnect and a power shutdown of the particular Disk FileModule.

The power supply unit 58 is also of conventional form and provides powerfor the Disk File Module or power for a plurality of Disk File Modules.In order to render this system independent of the AC power distributionsystem, a DC converter is used to supply the various required voltages;thus, the converter can be supplied with a 12 volt DC input and wouldgenerate a plus or minus 24 volt output, a plus or minus 12 volt outputand a plus or minus 5 volt output.

The entire preferred system can operate in an environment wheretemperatures are kept between 40° Fahrenheit and 100° Fahrenheit and thehumidity is less than 90%.

In the past the mechanical complexity of disk pack drives and theexposure of their most critical components to environment hadconsiderably limited the reliability of these drives. By enclosing thecritical components in a sealed module, and by limiting the componentssubject to friction and wear to the two precision bearings in themotor-spindle, the reliability of the disk system is now increased by alarge order of magnitude. Thus, now the mean time between failures maytypically be better than 10,000 hours. Further, when a failure occurs,the mean time to repair the units with a replacement module by asemiskilled person can be less than one-half hour.

The failure of an internal component of a Disk File Module would requireexchanging the module and sending it to a specially equipped servicecenter. If necessary the information can be retrieved from the disk ofthe impaired Disk File Module provided that there was no catastrophicdisk crash which occurred on all the bands of recorded information. Thisrecovery can be accomplished by mounting the disk together with itsrotor and rotor frame on a special drive which can position read headsover the information tracks with the help of a track-follower servo.

The mechanical arrangement of the Disk File Module lends itself to highsystem flexibility without major redesign. Up to three additionalindependent voice-coil actuators, which operate in a synchronousrelationship, can be added to a single Disk File Module, so that theremay be at least four actuators all synchronously operative fortransducing operations with the magnetic disk. Also as discussedpreviously, there is the flexibility which provides for a "mix" oftransducing systems wherein there can be a plurality of positionabletransducing systems controlled by the above-described type actuator andthis can be combined with one or more fixed-head-per-track systems whichmight be desired for the accessing of certain special informationtracks.

The storage capacity dedicated per channel can typically vary from 80million bits to 360 million bits for the actuator channels. All fouractuator channels of the Disk File Module have independent Read/Writeand access capabilities; thus, in the Electronic Module 50E there is aData Channel Control for each actuator channel and an additionalActuator Servo Control for each voice-coil actuator assembly 30.

Another flexible aspect of the system is the possibility of introducingfurther cooling means into the system by placing, for example, asquirrel cage impeller on the shaft 21_(s). This can be combined with apositive filter pressurized air system which can be easily fitted ontothe underside ribbing of the Disk File Module.

Under normal conditions the metallic base plate casting 10_(b) and themetallic flanges 7_(f1), 7_(f2), 7_(f3), 7_(f4) provide means forconducting away the heat generated internally. However, a greater amountof internal cooling capacity can be accomplished by the above-referencedair circulation system without any substantial change in the designconfiguration of the Disk File Module. Another means for facilitatingcooling within the scope of the present design is to make the top cover10_(a) of metallic material which will also help conduct heat away fromthe internal system.

Having thus described a low-mass, fast-access short stroke, voice-coilmotor actuator which is used with a sealed unitized Disk File Module,the following claims are made:

What is claimed is:
 1. A voice-coil actuator system comprising:a. a mainmagnetic circuit having a pole shoe and a magnet forming an air gap; b.a voice-coil residing and moving totally within said air gap; c. meansfor supporting said voice-coil; d. means for developing a signal forsensing motion of, direction of, and velocity of, said voice-coilincluding:d-1. means for obviating the effect of changing magneticfields due to voice-coil motion in said air gap of said main magneticcircuit.
 2. The actuator system of claim 1 wherein said main magneticcircuit includes:e. an annular ring magnet having first and second polarfaces; f. a cylindrical pole of magnetic material placed axially withinsaid central opening of said annular ring magnet, said cylindrical polehaving extending flanges at one end to form a base plate which abutsagainst the periphery of said first polar face of said annular ringmagnet; g. an annular pole piece of laminated magnetic material which isplaced to abut the second polar face of said annular ring magnet andforming an annular air-gap between itself and one end of saidcylindrical pole; h. and wherein said cylindrical pole has an axialbore-opening therethrough.
 3. The voice-coil actuator system of claim 2,wherein said means for developing a signal includes:d-2. a differentialvelocity transducer mounted concentrically in and around said axialbore-opening of said cylindrical pole material, said differentialvelocity transducer including:d-2a. a central support rod passingthrough said axial bore-opening of said cylindrical pole material, saidcentral support rod carrying a pole magnet having its poles oriented inthe axial direction; d-2b. a first and second coil of stationarywindings encompassing the axial bore-opening of said cylindrical polematerial; d-2c. said central rod carrying a bobbin which supports saidvoice coil within the air gap between said annular pole piece and saidone end of said cylindrical pole material.
 4. The voice-coil actuatorsystem of claim 3 wherein saidfirst and second coil windings are wounddifferentially and encompassed by a magnetic shield to prevent anymagnetic interference from any fields other than that of the saidaxially-oriented pole magnet in said axial boreopening, and said meansfor supporting said voice-coil comprises an axially movable integratedunit including:said central support rod, said axially located polemagnet, said bobbin for mounting said voice-coil, a pair of springflexures holding said central support rod, whereinthe periphery of saidflexures are anchored, an extension-arm for holding a plurality oftransducing heads.
 5. A voice-coil actuator and positioner unitcomprising:a. a main magnetic circuit means made of a magnet andmagnetic material in a cylindrical configuration and having pole facesand producing a magnetic field across an annular air gap; b. a centralbore-opening residing centrally and axially within said magnetic circuitmeans; c. a voice-coil residing and moving totally within said annularair gap; d. a bobbin, on which is mounted said voice-coil; e. adifferential velocity transducer mounted around and within said centralbore-opening and including:e-1. a central support rod capable oflongitudinal and rotary motion, said support rod holding said voice-coilbobbin; e-2. a first and second coil winding encircling the periphery ofsaid central bore-opening; e-3. a pole magnet held by said support rodand residing within said bore-opening with the first and second poles ofsaid pole magnet being locationally oriented within the central area ofthe axis of the respective first and second coil windings; e-4. saidfirst and second coil windings being connected differentially so as toprovide an electrical signal representative of the velocity,acceleration and direction of said pole magnet, which pole magnet movesin coordination with movement of said voice-coil; f. first and secondspring flexures holding said center support rod; g. an extension armsupported by said central support rod.
 6. The actuator and positionerunit of claim 5 wherein said differential velocity transducer includes amagnetic shield around the periphery of said first and second coilwinding.
 7. The actuator of claim 5 including:a. a plurality oftransducing head units residing on said extension arm wherein saidextension arm includes a pivot around which one edge of said extensionarm may be elevated or depressed; b. a solenoid for imparting rotarymotion to said central rod; c. a cam connected to said central rod; d.said cam being placed in proximity to one end of said extension arm andcapable of causing a pivoting action to said extension arm.
 8. Theactuator of claim 5 wherein said air gap separating the pole faces has alength greater than the axial length of said voice-coil; andwherein noportion of said voice-coil moves beyond the said annular air gap.
 9. Anelectromagnetic actuator and transducer positioner comprising:a. meansfor supplying a magnetic field; b. an air gap having magnetic fluxprovided by said means for supplying said magnetic field; b1. avoice-coil residing and moving within said air gap; c. an axial borewithin said means for supplying a magnetic field; d. a differentialvelocity transducer located around the periphery of said axial bore andwithin including:d-1. first and second coil windings around theperiphery of said axial bore; d-2. a magnetic encompassing the peripheryof said first and second coil windings; d-3. a central rod, movablewithin said axial bore, said rod carrying:d-3a. pole magnet whose northand south poles reside and move within the interior of said respectivefirst and second coil windings; e. said central rod also carrying:e-1. abobbin which supports said voice-coil winding within said air gap; e-2.an extension arm for holding a plurality of transducing heads; e-3. aplurality of transducing heads; f. a first and second spring flexure forsupporting the extremities of said central rod and permitting axialmotion of said rod; g. means for providing electrical signals to saidvoice-coil for repositioning the position of said transducer heads. 10.The actuator of claim 9 wherein:h. said bobbin includes a pivot forpermitting rotation of said extension arm.
 11. The actuator of claim 10including:i. means for rotating said central rod; j. means for elevatingand/or depressing said extension arm.
 12. The actuator of claim 11wherein said means for rotating said central rod inclues a solenoid;andsaid means for elevating/depressing said extension arm includes a camconnected to and responsive to rotation of said central rod.
 13. Anelectromagnetic actuator comprising:a. means for developing a magneticfield across an air gap; b. an axial bore within said means fordeveloping said magnetic field; c. a bobbin, movable within said airgap; d. a coil wound around said bobbin; e. a differential velocitytransducer, encompassing said axial bore, for developing a signalrepresentative of the motion of said coil and bobbin, said transducerincluding:e-1. a magnetic shield which encompasses said transducer; e-2.a central rod, movable longitudinally, which supports said bobbin andvoice coil; e-3. a first and second winding, wound differentially, andencompassing said axial bore, for sensing motion of a pole magnet withinsaid axial bore;e-4. a pole magnet within said central movable rod; f. aplurality of flexures for holding said movable rod in a longitudinalposition yet permitting a limited amount of forward and reverse motion;g. wherein no portion of said coil ever moves beyond the space of saidair gap; and h. wherein said central rod is rotatable in said axialbore; i. means to rotate said central rod.
 14. In a voice-coilpositioner for transducing heads in a magnetic disk system, thecombination comprising:a. a cylindrical form of magnetic materialforming a magnetic circuit and including:a-1. a magnet, a-2. a main airgap, a-3. a central and axial bore-opening, b. a voice-coil windingresiding and moving only within said main air gap; c. a movable bobbinfor supporting said voice-coil winding, said bobbin carrying:c-1. anextension arm, c-2. a plurality of transducer heads on said extensionarm, d. first and second spring flexures having centers mounted inalignment with the axis of said central bore-opening; e. a movablecentral rod residing within said central bore opening and supported atits extremities by said first and second spring flexures; f. adifferential velocity transducer which includes:f-1. first and secondcoil windings connected differentially and placed annularly around saidcentral bore opening, f-2. a bar-magnet mounted on said central movablerod and having a north pole and a south pole, said bar-magnet being sonormally oriented such that one pole of said magnet resides and moveswithin the interior of one of said differential coil windings and theother pole of said bar-magnet resides and moves within the interior ofsaid second of said differential coil windings, f-3. said movablecentral rod within said central bore being integrally connected with andsupporting said bobbin, f-4. wherein said first and said seconddifferential coil windings develop a signal sensitive to the motion ofsaid voice-coil but which cancel out any extraneous fields due to motionof said voice-coil within the main air gap and magnetic field of saidvoice-coil magnetic circuit.